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Understanding Cells: Structure, Function, and Roles in Life

Chapter 3 delves into the fascinating world of cells, the basic unit of life. It explores cytology, the study of cells, their structure, and functions, including metabolism, responsiveness, growth, and reproduction. The chapter highlights the significance of cells in forming tissues and powering all bodily activities. It examines various organelles within the cell, like the nucleus, mitochondria, and endoplasmic reticulum, and explains protein synthesis driven by DNA and RNA. Insights into microscopy techniques for cell study are also presented.

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Understanding Cells: Structure, Function, and Roles in Life

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  1. Chapter 3Cells & Their Functions

  2. The Role of Cells • Basic unit of all life • Cytology – the study of cells • Simplest structure that shows all the characteristics of life such as • Organization • Metabolism • Responsiveness • Homeostasis • Growth • Reproduction

  3. The Role of Cells • It is possible for a single cell to live independently of other cells • Protozoa • bacteria • Cells make up all tissues • All activities of the human body result from the activities of individual cells

  4. Microscopes • Stains – dyes that color cells and tissues to aid viewing • Compoundlight microscope • Magnifies 1000 times • 2 lenses • Uses visible light for illumination • Transmission electron microscope • 1,000,000 times magnification • Uses electron beam instead of light • Scanning electron microscope • 100,000 times magnification • Shows surface features, but in 3D view

  5. Cell Structure • All cells share certain characteristics. • Main parts: • Plasma membrane • Nucleus • Cytoplasm • Organelles

  6. Plasma Membrane • Formerly called the cell membrane • Function • Encloses the cell • Participates in growth & reproduction • Involved in cellular interactions • Regulates what enters and leaves the cell

  7. Plasma Membrane • Bilayer structure • Phospholipids • Cholesterol • Carbohydrates • Proteins • Channels • Transporters • Receptors • Enzymes • Linkers • Cell identity markers

  8. Plasma Membrane Proteins • Channels pores that allow specific ions to enter or leave • Transporters shuttle substances across the membrane • Receptors act as points of attachment for materials that act on the cell • Enzymes participate in reactions occurring at the plasma membrane • Linkers give structure to the membrane and help cells attach to each other • Cell identity markers are proteins that are unique to an individual’s cells. Important in immunity & tissue transplants

  9. Cell Nucleus • Nucleus is the biggest organelle in the cell • Organelles – specialized structures that perform different tasks for the cells • Control center of the cell • Contains chromosomes which govern all cellular activities • Nucleolus contains RNA, DNA, and proteins and manufactures ribosomes in the cytoplasm • Almost all DNA is found in the cell nucleus

  10. The Cytoplasm Cytosol – liquid part of cytoplasm containing nutrients and organelles such as: • Endoplasmic reticulum • Ribosomes • Mitochondria • Golgi apparatus • Lysosomes • Peroxisomes • Vesicles • Centrioles

  11. Endoplasmic reticulum Network of membranes that is either smooth or rough • Smooth ER – involved in lipid synthesis • Rough ER – comes from ribosomes attached to the ER • Ribosomes – necessary for protein synthesis and are either attached to ER or floating free

  12. Cell Organelles Cont. • Mitochondria – converts nutrients into ATP, the power plant of the cell. Active cells have more mitochondria than other cells • Golgi Apparatus – involved in sorting and modifying proteins and then packaging them for export from the cell • Centrioles - near the nucleus; help to organize the cell and divide the cell contents during the process of cell division

  13. Cell Organelles Cont. • Lysosomes – remove waste and foreign materials from the cells • Peroxisomes – destroy byproducts of metabolism • Vesicles – storage units of the cell, can also move materials into and out of cells

  14. Surface Organelles • Cilia – small hair-like projections that wave, creating movement of fluids around the cell. Respiratory passage cells have cilia and cells in the female reproductive tract. • Flagellum – long whip-like extension for movement. The only cells in humans with flagella are sperm cells.

  15. Cellular Diversity • Size • Average size is 10-15 micrometers • RBCs are small – 7 micrometers • Muscle cells are big – 200 micrometers • Composition – most human cells have all the organelles. Some cells have more than one type of organelles than another due to their function

  16. Protein Synthesis: Chromosomes & Genes • Chromosomes are the hereditary units that govern cells • 23 pair, 46 total • Divided into genes • Genes carry the messages for the development of particular inherited characteristics and do so by directing the manufacture of proteins in the cell.

  17. DNA & RNA • Genes are made of DNA – deoxyribonucleic acid • DNA is composed of nucleotides • RNA – Ribonucleic acid – a related compound which participates in protein synthesis but is not part of chromosomes • RNA is composed of nucleotides

  18. DNA & RNA Composition • DNA is composed of • 4 nucleotides • Adenine (A) • Guanine (G) • Cytosine (C) • Thymine (T) • RNA is composed of • 4 nucleotides • Adenine (A) • Guanine (G) • Cytosine (C) • Uracil (U)

  19. NucleotideStructure • Composed of three units • Sugar – • RNA – ribose • DNA - deoxyribose • Phosphate - an area containing phosphorus • Nitrogen base – an area containing nitrogen

  20. Deoxyribose & Ribose

  21. DNA Structure • DNA is built like a ladder • Sugar-phosphate backbone • Nitrogen bases are the steps • 2 DNA strands make a pair • Nucleotide adenine always pairs with thymine • Guanine always pairs with cytosine • 2 DNA strands are bonded together with hydrogen bonds – form double helix

  22. RNA • RNA interprets the information from the DNA blueprint to synthesize proteins • RNA is found almost entirely in the cytoplasm • RNA is a single strand of nucleotides • There are 3 types of RNA • mRNA – messenger RNA • rRNA – ribosomal RNA • tRNA – transfer RNA

  23. The Role of RNA Protein synthesis • Transcription • Messenger RNA (mRNA) • Translation • Transfer RNA (tRNA) • Ribosomal RNA (rRNA)

  24. Protein Synthesis and RNA • DNA breaks its bonds and uncoil into single strand • Transcription – transfer of information from DNA to mRNA in the nucleus >> matching RNA strand forms based on pairing • mRNA leaves the nucleus and travels to a ribosome in the cytoplasm

  25. Transcription.

  26. Translation.

  27. Cell Division • Meiosis • Sex cells • Mitosis • Somatic cells

  28. Cell Division - Mitosis • Mitosis – the process of cell division where an original parent cell becomes two identical daughter cells • Before mitosis can occur, DNA must double – therefore, the 46 chromosomes in the nucleus must double

  29. Interphase • The stage of life in a cell between one mitosis and the next • During this phase, DNA uncoils and each strand takes on a matching strand of nucleotides to make up 2 new DNA strands, each one identical to the original and each other • The new, uncoiled DNA strands are held in the centromere until mitosis • A typical cell spends most of its cycle in interphase and a relatively short time in mitosis

  30. Mitosis • 4 stages • Prophase • Metaphase • Anaphase • Telophase

  31. Mitosis - Prophase • The new double strands of DNA coil tightly into a double helix • The nucleolus and the nuclear membrane begin to disappear • All other organelles disappear except those needed for mitosis • Two centrioles in the cytoplasm move towards opposite ends of the cell • Thin spindle fibers begin to form between the centrioles

  32. Mitosis - Metaphase Chromosomes attach to spindle fibers and line up across the center of the cell

  33. Mitosis - Anaphase The centromere splits and the duplicated chromosomes separate and begin to move towards opposite ends of the cell

  34. Mitosis - Telophase • A membrane appears around each group of separated chromosomes, forming 2 new nuclei • The plasma membrane pinches off to divide the cell

  35. Mitosis : Summary • At the end of mitosis there 2 new cells • Each daughter cell has exactly the same DNA as the original • All organelles reappear in the daughter cells

  36. Movement of Substances Across the Plasma Membrane Travel across the membrane is based on several factors: • Molecular size • Solubility • Electrical charge

  37. Movement That Does Not Require Cellular Energy Passive transport • Diffusion • Osmosis • Filtration • Facilitated diffusion

  38. Diffusion • Concentration gradient - constant movement of particles from a region of higher concentration to one of lower concentration • Equilibrium - diffusing substances spread throughout available space until their concentration is equal everywhere • Passage is limited to those particles small enough to pass through spaces between molecules of the plasma membrane

  39. Osmosis • The diffusion of water through a semi-permeable membrane • Water moves from an area where there is more water molecules to an area where there is less water molecules • The solvent water moves from an area of lower solute concentration to an area of higher solute concentration • Water follows salt

  40. Osmotic Pressure • Describes the tendency of a solution to draw water into it • Directly related to concentration: the higher the concentration of a solution, the greater the tendency to draw water in • A measure of the force driving osmosis • Determined by applying enough pressure to the surface of a liquid to stop the flow of water by osmosis

  41. Filtration • Passage of water containing dissolved materials through a membrane as a result of a “pushing” force on one side • Movement of materials out of the capillaries and into the tissues under the force of blood pressure • Movement of materials out of the blood and into urine in the kidneys

  42. Facilitated Diffusion • Movement of materials across the plasma membrane in the direction of the concentration gradient but using transporters to move the material at a faster rate • Glucose

  43. Movement That Requires Cellular Energy Active transport • Bulk transport or vesicular transport • Endocytosis • Phagocytosis • Pinocytosis • Exocytosis

  44. Active Transport • Moves solute particles in or out of the cell opposite of the direction they would normally flow by diffusion • Transporters – proteins in the plasma membrane that are required to transport the particles • Nerve and muscle cells depend on active transport of Na, K and Ca for proper function

  45. Endocytosis – bulk transport of large quantities of materials into or out of the cells • Phagocytosis – large particles are engulfed by the plasma membrane and moved into the cell • White blood cells rid the body of foreign materials • Pinocytosis – cell membrane engulfs droplets of fluid

  46. How Osmosis Affects Cells • Isotonic – solutions with concentrations equal to the concentration of the cytoplasm • Blood plasma, interstitial fluid, normal saline (0.9% salt), 5% dextrose • Hypotonic – a solution less concentrated than intracellular fluid • A cell in hypotonic solution will draw water in and may burst • Hemolysis – a red blood cell drawing too much water in and bursting • Hypertonic – a solution more concentrated than intracellular fluid • Crenation – the process by which a cell that loses water to surrounding fluids and shrinks

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